Conditioning of cellulose fiber and the product thereof



Patented Sept. 27, 1932 ym'rso STATES PATENT OFFICE MILTON O. SGHUR, ROYAL H. BASCH, AND BENJAMIN G. 005, of BERLIN, NEW HAMP- SHIRE, ASSIGNOBS T0 BROWN ."POBATION OF MAINE COMPANY, OF BERLIN, NEW HAMPSHIRE, A COB- GONDI'IIONIN'G 0F CELLULOSE FIBER AND THE PBOD UCT THEREOF No Drawing.

This invention relates to conditioning,

prior to nitration, of cellulose fiber to 'produce a product useful for the manufacture of films, lacquers, artificial silk, and the like.

Before cellulose fiber is subjected to nitration, it has sometimes been found desirable to condition-the fiber so as to make possible high yield and good quality of nitrated product. For instance, in application Serial No. 140,674, filed October 9, 1926, by George A. Richter, Milton 0. Schur, and Royal H. Rasch, there are disclosed various methods of treating the fiber so as to retard the action of the nitrating acid, as it has been found that improved results are thereby realized. Nitration may be retarded, as by beating the fiber, treating it with nitrocellulose, or otherwise suitably lowering its absorptivity, as by sheeting into tissue paper and subjectlng to heavy pressure before drying. The theory advanced in that. application is that the sulphuric acid in the nitrating bath tends to hydrolyze the cellulose fibers, especially when the pulp is highly absorptive. If, however, the fiber is first treated with nitrocellulose or is otherwise rendered less absorptive, the side reaction is apparently retarded or avoided and nitration proceeds smoothly. The coating or film of nitrocellulose on the fibers probably permits nitric acid to penetrate into the fiber wall more easily than sulphuric acid, and perhaps readily allows water generated within the fiber during nitration to diffuse into .the main body of the nitratin acid, so that within the fiber wall there is elieved to be a nitric-acid-rich mixture which has a greatly reduced hydrolyzing efiect and nitrates the cellulose before hydrolysis can proceed to any troublesome degree. .It is well known, for example, that nitrating acids rich in nitric acid give high yields, but that acids rich in sulphuric acid cause hydrolysis and correspondingly low yields. The film of nitrocellulose on the fibers, by slowing up the reaction, eliminates local over-heating in the'acid bath, and thus prevents loss in yield, for the higher the temperature of nitration, the eater is the tendency for the yield to drop ause of side reaction. When using fiber in the form of tislpplication filed December 14, 1928. Serial No. 826,150.

sue, another function of the nitrocellulose is to cement the loosely adhering surface fibers to the body of the paper, thereby counteracting the tendency of the nitrated surface fibers to pass into solution in the nitrating acid and become lost during the separation of the spent acid from the nitrocellulose in the centrifuge.

We have discovered that if cellulose fiber is treated with an organic solvent of substances such as the resins or waxes naturally occurring therein, and then evaporated from the fiber, the yield of nitrated product is notably increased and when the product is dissolved in suitable media, solutions of remarkable clarity and sparkle are produced. Upon making this discovery, we at first found it diflicult to account for the surprising results secured, but study and research indicate a consistency between these results and the theory which we have advanced.

Our conclusion is that a solvent of the character described, when evaporated from cellulose fibers, deposits on the surface of the fibers a film of the resinous or waxy materials naturally occurring therein, and that the film acts in a manner similar to a nitrocellulose film deposited on the fiber before nitration as heretofore described. We were led to this conclusion through the observation that the fibers after treatment with such solvents absorb water less readily than previously, that solvents of widely different characteristics produce similarresults that the initial temperature rise in the nitrating shredded wood pulp or tissue with solvent,

followed by the evaporation -of the solvent, results in an increase in yield of nitrated product, and that improved results are sei .45 But traces of resinous and waxy material j are left in the-fiber because of practicallimitations in 'a'refin'ing process, and since only 5 use non-inflammable solvents, such as carbon tetrachloride, particularly when the fiber is subjected to vapors of the solvent, thus avoiding explosion and fire hazard. When the fiber isone having c mparatively high resin content, such as sulphite pulp, the

solvent treatment may be carried out so as to effect an extraction and removal of a portion of the resin, sufficient resin being left so that when the solvent is evaporated, an acid-repellent film which retards nitration of the fiber is left on its surface. The fiber may be immersed in bulk form in the solvent or passed throu h a bath of solvent as a continuous sheet 0 tissue, under conditions resultin 'in an extraction of resinous, waxy, and o lyimpurities from the fiber, so that nitrocellulose or high stability .and freedom fromv coloring matter may be prepared there.- from. Whilesuc'h impurities may besubstantially completely removed from the fiber, there is a trace ofresinous and waxy material left after anypractical treatment, this 'trace iapparently being deposited on the surfac'e of. the fiber when the solvent is evaporated;-:;.;!1his trace is ordinarily negligible 'withijregard to imparting color, cloudiness, instability etc, to the nitrocellulose pre- .paredfroln'fthefiber,"and from this viewpoint the-fiber maybeproperly described as I having been "substantially completely free from resinous and waxy material. From the viewpoint of yield, however, the presence of minute residue on the surface of the fiber is of ,highjadaantagei, In the-case otwood pulp which has been refined to high alpha cellulose "content, as by boiling in an alkaline liquor containing soap, non-alpha cellulose impurities, including beta and gamma cel-, luloses, lignin,'resinous,'waxy, and oily substance, are largely-removed from the fiber.

traces are needed toform an acid-repelling on the fibers, it becomes possible, through-the expedient-of-treati ng the fiber witha solvent','to put the residual waxy mawhen al tissue of the refined wood fiber is I dipped in solvent, the solvent. evaporated, f the tissue jnitrated, it is found that, a

noteworthy increase in'yield of nitrocellu- "lose is efiected. Inasmuch as the refined fiber contains only traces of waxy or resinousmaterial, very littl'e extraction of such material -"is effected when 'atissue of such fiber is dipped in solvent ,for a short time. The [treatment withlsolventmay :be efi'ected under various-temperature-conditions, the sol terial v to" advantageous use. For instance,

vent being from room temperature to its boiling point, or in the form of a vapor.

Below is a table showing the yield of nitrocellulose obtained after sheets of waterleaf tissue made of a wood pulp of high alpha cellulose content were dipped for a second or two in various solvents at room temperature, dried, and bone-dried at 100 to 103 C. prior to nitration:

Iso-amyl alcohol 154.2 Iso-amyl acetate 154.3 'Ethera 153.3 Alcohol (98%) 154.0 Chloroform 153.7 Trichlorethylene ..154.0 Gasoline 154.8 Kerosene 154.2 Benzol 154.2 Benzol-acetone 1555-1525 tion. '.Thus, mixtures of solvents may sometimes be used to better'advantag'e than one solvent alone. For instance, although acetone by itself raises the yield very little, it may be used as a comparatively inexpensive vehicle to carry the much more efiective but more expensive iso-amyl acetate through a paper sheet. Beneficialfefiects may also be obtained by passing a sheet of dry paper through a chamber containing air heavily charged with vapors of the solvents.

While the process of the present invention may be employed in preparing cellulose fibers of various origins for nitration, it may be applied to especial advantage in the case of wood pulp, as suchfiber may be improved more markedly as a .raw material for nitration than cotton, fiber. We have in mind more particularly a wood pulp which has been refined to high alpha cellulose content, as such pulp yields nitrocelluloses comparable in quality with those prepared from cotton fiber. Such pulp, however, may fail under some circumstances to give as high a yield of nitrocelluloses as cotton "fiber, but'by treating such refined wood pulp with solvents as herein described, it is possible to raise the [yield of nitrocellulose to a substantially theoretically perfect value.

fI-Iaving thus described certain modes of practising the process of this invention, it should be evident to'those skilled in the art that various changes'and modifications, might be made therein without departing from the spirit or scope of invention as defined by the appended claims.

We claim:

1. A process which comprises treating cellulose fiber with an organic solvent of a substance naturally occurring therein, evaporating the solvent from the whole surface of the fiber, and nitrating the fiber.

2. A process which comprises wetting cellulose fiber with an organic solvent of a substance naturally occurring therein, evaporating the solvent from the whole surface of the fiber, and nitrating the fiber.

3. A process which comprises wetting cellulose fiber with a non-inflammable organic solvent, evaporating the solvent from the gholesurfaceof the fiber, and nitrating the ber.

4. A process which comprises dipping a tissue of cellulose fiber into an organic solvent of a substance naturally occurring therein, evaporating the solvent from the whole surface of the tissue, and nitrating the tissue.

5. A process which comprises wetting wood pulp with an organic solvent of the resinous and waxy materials naturally occurring therein, evaporating the solvent from the whole surface of the fiber, and nitrating the 111 p 6? A process which comprises immersing a tissue of wood pulp in a bath-of an organic solvent of the resinous and waxy materials naturally occurring in such pulp, evaporating the solvent from the whole surface of the tissue and nitrating.

7. A dry, waterleaf paper which has undergone previous treatment with an organic solvent of residual resinous and waxy material associated with the cellulose fibers constituting such paper and then dried to evaporate said solvent from the whole surface of said paper, whereby said surface is enriched with resinous and waxy material.

8. A dry, waterleaf paper composed of wood pulp and which has undergone previous treatment with an organic solvent of residual resinous and waxy material associated with the pulp fibers and then dried to evaporate said solvent from the whole surface of said paper, whereby said surface is enriched with resinous and waxy material.

9. A dry, waterle'af paper composed of wood pulp of high alpha cellulose content and which has undergone previous treatment with an organic solvent of residual resinous and waxy material associated with the pulp fibers and then dried to evaporate said solvent from the whole surface of said paper, whereby said surface is enriched with resinous and waxy material.

10. A process which comprises treating cellulose fiber with an organic solvent of a substance naturally occurring therein while substantially keeping said substance in said fiber, evaporating the solvent from the whole surface of the fiber, and nitrating the fiber.

11. A process which comprises treating refined wood pulp with an organic solvent of the resinous and waxy substances naturally occurring therein while substantially keeping said substances in said pulp, evaporating the solvent from the whole surface of the fiber, and nitrating the pulp.-

l2. Cellulose fiber wherein resinous and waxy constituents have merely undergone migration to its surface through treatment with a solvent for said constituents, and drying its entire surface while'keeping said constituents in said fiber.

13. Refined wood pulp wherein residual resinous and waxy constituents have merely undergone migration to its surface through treatment with a solvent for said constituents, and drying its entire surface while keeping said constituents in said pulp.

14. A tissue of cellulose fiber wherein resinous and waxy constituents have merely undergone migration to its surface through treatment of said tissue with a solvent for said constituents, and drying its entire surface while keeping said constituents in said tissue.

15. A tissue of refined wood pulp wherein residual resinous and waxy constituents have merely undergone migration to its surface through treatment of said tissue with a solvent for said constituents, and drying its entire surface while keeping said constituents in said tissue.

In testimony whereof we have aflixed our signatures.

MILTON O. SCHUR. ROYAL H. RASCH. BENJAMIN G. HOOS. 

